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Two-dimensional (2D) layered materials with unique physicochemical properties, such as graphene, transition metal dichalcogenides, and hexagonal boron nitride, have shown considerable potential in the electrical and electronics industries as well as society. To realize the practical applications of 2D materials, the size, shape, and edge structures must be refined. Etching is a critical processing step in the semiconducting industry and its potential as an efficient approach for fabricating diverse nanostructures of 2D materials has been demonstrated, broadening their applications in the field of nanoelectronics. In this paper, we present an overview of recent advances in anisotropic etching of various 2D materials. Anisotropic etching and the associated mechanisms are discussed in context of the synthesis, processing, and characterization of 2D materials. An overview of the applications of anisotropic etched 2D materials is provided. Finally, the challenges and future opportunities for anisotropic etching of 2D materials are discussed.

Surface treatment is a pivotal technique for enhancing the properties of industrial-grade bulk c-silicon wafers, revolutionizing their applicability in both PV and MEMS applications. In this paper we presents a brief overview of recent advancements in anisotropic etching methodologies, elucidating their role in tailoring surface morphology, roughness, and texturing of silicon wafers with precision and control. Fundamental insights into the chemical reactions governing the anisotropic etching process are explored, highlighting its capacity to produce intricate surface structures beneficial for light management in PV cells and optimized mechanical characteristics for MEMS devices. Encompassing diverse anisotropic etching solutions and their effects on surface morphology, addressing the intricate interplay between etchant composition, temperature, and process duration. Strategies for achieving superior selectivity, reproducibility, and uniformity across large-scale silicon wafers are discussed, elucidating the nuanced control required for industrial implementation. [ABSTRACT FROM AUTHOR]

This article discusses a method for forming black silicon using plasma etching at a sample temperature range from −20 °C to +20 °C in a mixture of oxygen and sulfur hexafluoride. The surface morphology of the resulting structures, the autocorrelation function of surface features, and reflectivity were studied depending on the process parameters—the composition of the plasma mixture, temperature and other discharge parameters (radical concentrations). The relationship between these parameters and the concentrations of oxygen and fluorine radicals in plasma is shown. A novel approach has been studied to reduce the reflectance using conformal bilayer dielectric coatings deposited by atomic layer deposition. The reflectivity of the resulting black silicon was studied in a wide spectral range from 400 to 900 nm. As a result of the research, technologies for creating black silicon on silicon wafers with a diameter of 200 mm have been proposed, and the structure formation process takes no more than 5 min. The resulting structures are an example of the self-formation of nanostructures due to anisotropic etching in a gas discharge plasma. This material has high mechanical, chemical and thermal stability and can be used as an antireflective coating, in structures requiring a developed surface—photovoltaics, supercapacitors, catalysts, and antibacterial surfaces. [ABSTRACT FROM AUTHOR]

We demonstrate a facile and safe anisotropic gas etching technique for β-Ga2O3 under atmospheric pressure using forming gas, a H2/N2 gas mixture containing 3.96 vol% H2. This etching gas, being neither explosive nor toxic, can be safely exhausted into the atmosphere, simplifying the etching system setup. Thermodynamic calculations confirm the viability of gas-phase etching above 676°C without the formation of Ga droplets. Experimental verification was achieved by etching ([Formula: see text]02) β-Ga2O3 substrates within a temperature range of 700–950°C. Moreover, selective-area etching using this method yielded trenches and fins with vertical and flat sidewalls, defined by (100) facets with the lowest surface energy density, demonstrating significant anisotropic etching capability.

The quartz crystal microbalance (QCM) biosensor is one of the devices that enables label‐free evaluation of biomolecular reactions. Commercial QCM biosensors have less than 10 channels for detection and are not suitable for the screening. The sensitivity of the QCM biosensor increases as the quartz thickness becomes thinner; however, the limit of thinning is 60–330 μm. In this study, applying micromachining technology, a QCM sensor array chip of 15 mm square that had 100 ultra‐thin quartz resonators (2.5 μm) that were operated wirelessly was developed. And we succeeded in detecting the resonance spectrum through the device evaluation. © 2024 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC. [ABSTRACT FROM AUTHOR]

Synthetic diamond crystallites were successfully etched by MnO2 powder. The effect of etching behavior on the surface morphology and properties of the treated diamond crystallites was investigated. Results showed that the etching intensity of both {100} and {111} planes increased as temperature increases, and the {111} plane was etched more significantly than the {100} plane under the same conditions. After etching, the morphology of etched pits on the {100} plane transformed from quadrilateral to octagonal, while those on the {111} plane were distinguished by triangular conical bulges. The compressive strength of a single diamond particle declines from 255 to 202 N, and the impact toughness decreases from 90.11% to 86.3%. More significantly, compared with raw diamond, the maximum flexural strength of the Cu-matrix bonding diamond block with etched diamonds increased from 394.2 to 464.9 MPa, an increase of 17.9%, and the cutting ratio of the diamond saw blades decreases from 17.5 to 9.67 g/m2. The ability to produce an anchoring connection between the etched diamond and the matrix accounts for the performance increase in diamond tools. The etching mechanism is a reaction between MnO2 and the C atom on the diamond surface. [ABSTRACT FROM AUTHOR]

This work is devoted to the technological features of creating an array of pyroelectric nanoparticles placed in the pores of a silicon oxide membrane, ensuring their thermal insulation both from each other and from the supporting substrate. Mechanisms of anodic oxidation of the Al/Ti/SiO2 structure, ensuring the self-organization of a nanostructured oxide mask with specified geometric parameters, have been established. It has been shown that from a certain thickness of the adhesion layer, overgrowing of the open areas of the mask with titanium oxide nanoparticles does not occur. The regularities of the method of local ion etching of multilayer structures are determined, which ensures control of the depth of the formed pores by controlling the ion current. A correlation has been established between the lateral size of the cavities in silicon and the aspect ratio of aluminum oxide pores. The possibility of forming a silicon oxide membrane with pyroelectric polymer nanoparticles embedded in its pores has been demonstrated.

This article discusses a method for forming black silicon using plasma etching at a sample temperature range from −20 °C to +20 °C in a mixture of oxygen and sulfur hexafluoride. The surface morphology of the resulting structures, the autocorrelation function of surface features, and reflectivity were studied depending on the process parameters—the composition of the plasma mixture, temperature and other discharge parameters (radical concentrations). The relationship between these parameters and the concentrations of oxygen and fluorine radicals in plasma is shown. A novel approach has been studied to reduce the reflectance using conformal bilayer dielectric coatings deposited by atomic layer deposition. The reflectivity of the resulting black silicon was studied in a wide spectral range from 400 to 900 nm. As a result of the research, technologies for creating black silicon on silicon wafers with a diameter of 200 mm have been proposed, and the structure formation process takes no more than 5 min. The resulting structures are an example of the self-formation of nanostructures due to anisotropic etching in a gas discharge plasma. This material has high mechanical, chemical and thermal stability and can be used as an antireflective coating, in structures requiring a developed surface—photovoltaics, supercapacitors, catalysts, and antibacterial surfaces.

Herein, by choosing few‐nm‐thin two‐dimensional (2D) nanocrystals of MOF‐5 containing in‐planner square lattices as a modular platform, a crystal lattice‐guided wet‐chemical etching has been rationally accomplished. As a result, two attractive pore patterns carrying Euclidean curvatures; precisely, plus(+)‐shaped and fractal‐patterned pores via ⟨100⟩ and ⟨110⟩ directional etching, respectively, are regulated in contrast to habitually formed spherical‐shaped random etches on MOF surface. In agreement with the theoretical calculations, a diffusion‐limited etching process has been optimized to devise high‐yield of size‐tunable fractal‐pores on the MOF surface that tenders for a compatibly high payload of catalytic ReI‐complexes using the existing large edge area once modified into a free amine‐group‐exposed inner pore surface. Finally, on benefiting from the long‐range fractal opening in 2D MOF support structure, while loaded on an electrode surface, a facilitated cross‐interface charge‐transportation and well‐exposure of immobilized ReI‐catalysts are anticipated, thus realizing enhanced activity and stability of the supported catalyst in photoelectrochemical CO2‐to‐CO reduction. [ABSTRACT FROM AUTHOR]

Abstract Silicon bulk micromachining is extensively employed method in microelectromechanical systems (MEMS) for the formation of freestanding (e.g., cantilevers) and fixed (e.g., cavities) microstructures. Wet anisotropic etching is a popular technique to perform silicon micromachining as it is low-cost, scalable, and suitable for large scale batch processing, which are the major factors considered in the industry to reduce the cost of the product. In this work, we report the wet anisotropic etching characteristics of Si{111} in sodium hydroxide (NaOH) without and with addition of hydroxylamine (NH2OH). 10M NaOH and 12% NH2OH are used for this study. The effect of NH2OH is investigated on the etch rate, etched surface roughness and morphology, and the undercutting at mask edges aligned along direction. These are the major etching characteristics, which should be studied in a wet anisotropic etchant. A 3D laser scanning microscope is utilized to measure the surface roughness, etch depth, and undercutting length, while the etched surface morphology is examined using a scanning electron microscope (SEM). The incorporation of NH2OH in NaOH significantly enhances the etch rate and the undercutting at the mask edges that do not consist of {111} planes. To fabricate freestanding structure (e.g., microcantilever) on Si{111} wafer, high undercutting at mask edges is desirable to reduce the release time. Moreover, the effect of etchant age on the abovementioned etching characteristics are investigated. The etch rate and undercutting reduce significantly with the age of the modified NaOH. The present paper reports very interesting results for the applications in wet bulk micromachining of Si{111}.

The work aims to explore the anisotropic etching of synthetic diamond single crystal by rare earth oxide. Under the protection of nitrogen, synthetic diamond single crystals were etched by Pr6O11 powder at 750-950℃. The surface morphology, phase composition and etching mechanism of different crystal surfaces of diamond single crystal after etching were characterized and analyzed by means of scanning electron microscopy, thermogravimetric analysis, X-ray diffraction and Raman spectroscopy, and the changes of diamond properties before and after etching were characterized by surface roughness, single particle compressive strength and impact toughness. The results show that the etching degree and morphology of {100} faces and {111} faces of diamond by Pr6O11 are different. When the temperature is 750℃, Pr6O11 etches slightly diamond crystals. The etching intensifies with the increase of etching temperature, moreover the etching degree of diamond {111} faces is more serious than that of {100} faces. The morphologies of the etching pits of diamond {111} faces change from triangular etching pits to layered triangular ones, and {100} faces change from slight quadrilateral to honeycomb-like etching pits. The maximum etching depth of {100} face increases from 1.12 μm to 12.54 μm, while the maximum etching depth of {111} face increases from 0.3 μm to 2.11 mm. The compressive strength of single diamond particle decreases from 576.25 N of unetched diamond to the smallest value of 530.06 N, and the impact toughness decreases from 92.94 J/cm2to 88.53 J/cm2. The etching mechanism of diamond single crystal by Pr6O11 is catalytic graphitization before 885℃, and the catalytic graphitization and oxidation after 885℃.

Herein, by choosing few‐nm‐thin two‐dimensional (2D) nanocrystals of MOF‐5 containing in‐planner square lattices as a modular platform, a crystal lattice‐guided wet‐chemical etching has been rationally accomplished. As a result, two attractive pore patterns carrying Euclidean curvatures; precisely, plus(+)‐shaped and fractal‐patterned pores via ⟨100⟩ and ⟨110⟩ directional etching, respectively, are regulated in contrast to habitually formed spherical‐shaped random etches on MOF surface. In agreement with the theoretical calculations, a diffusion‐limited etching process has been optimized to devise high‐yield of size‐tunable fractal‐pores on the MOF surface that tenders for a compatibly high payload of catalytic ReI‐complexes using the existing large edge area once modified into a free amine‐group‐exposed inner pore surface. Finally, on benefiting from the long‐range fractal opening in 2D MOF support structure, while loaded on an electrode surface, a facilitated cross‐interface charge‐transportation and well‐exposure of immobilized ReI‐catalysts are anticipated, thus realizing enhanced activity and stability of the supported catalyst in photoelectrochemical CO2‐to‐CO reduction. [ABSTRACT FROM AUTHOR]

Traditional methods for synthesizing InGaN quantum dots (QDs), such as the Stranski-Krastanov growth, often result in QD ensembles with low density and non-uniform size distribution. To overcome these challenges, forming QDs using photoelectrochemical (PEC) etching with coherent light has been developed. Anisotropic etching of InGaN thin films is demonstrated here with PEC etching. InGaN films are etched in dilute H2SO4 and exposed to a pulsed 445 nm laser with a 100 mW/cm2 average power density. Two potentials (0.4 V or 0.9 V) measured with respect to an AgCl|Ag reference electrode are applied during PEC etching, resulting in different QDs. Atomic force microscope images show that while the QD density and sizes are similar for both applied potentials, the heights are more uniform and match the initial InGaN thickness at the lower applied potential. Schrodinger-Poisson simulations show that polarization-induced fields in the thin InGaN layer prevent positively charged carriers (holes) from arriving at the c-plane surface. These fields are mitigated in the less polar planes resulting in high etch selectivity for the different planes. The higher applied potential overcomes the polarization fields and breaks the anisotropic etching. [ABSTRACT FROM AUTHOR]

Silicon bulk micromachining is extensively employed method in microelectromechanical systems (MEMS) for the formation of freestanding (e.g., cantilevers) and fixed (e.g., cavities) microstructures. Wet anisotropic etching is a popular technique to perform silicon micromachining as it is low-cost, scalable, and suitable for large scale batch processing, which are the major factors considered in the industry to reduce the cost of the product. In this work, we report the wet anisotropic etching characteristics of Si{111} in sodium hydroxide (NaOH) without and with addition of hydroxylamine (NH2OH). 10M NaOH and 12% NH2OH are used for this study. The effect of NH2OH is investigated on the etch rate, etched surface roughness and morphology, and the undercutting at mask edges aligned along < 112 > direction. These are the major etching characteristics, which should be studied in a wet anisotropic etchant. A 3D laser scanning microscope is utilized to measure the surface roughness, etch depth, and undercutting length, while the etched surface morphology is examined using a scanning electron microscope (SEM). The incorporation of NH2OH in NaOH significantly enhances the etch rate and the undercutting at the mask edges that do not consist of {111} planes. To fabricate freestanding structure (e.g., microcantilever) on Si{111} wafer, high undercutting at < 112 > mask edges is desirable to reduce the release time. Moreover, the effect of etchant age on the abovementioned etching characteristics are investigated. The etch rate and undercutting reduce significantly with the age of the modified NaOH. The present paper reports very interesting results for the applications in wet bulk micromachining of Si{111}. [ABSTRACT FROM AUTHOR]

Plasma anisotropic etching polishing (plasma-AEP), a non-contact polishing method, is proposed to achieve highly efficient planarization of polycrystalline diamond (PCD) films. Inductively coupled plasma, with a high concentration of reactive radicals, serves as the source of plasma-AEP. In-situ observation confirms that the planarization effect of plasma-AEP is realized through the preferential removal of the top areas of the pyramid-shaped protrusions, despite the entire surface being uniformly irradiated by the plasma. The material removal rate in plasma-AEP for PCD achieves 127 μm/min. Plasma-AEP is proven effective for PCD films with thicknesses of 0.5, 1, and 2 mm, demonstrating a generic semi-finishing approach for PCD regardless of thickness. Atomic-scale nudged elastic band calculations revealed that the energy barriers for CO and CO 2 desorption from 1- and 2-coordinated C atoms are significantly lower than those for 3- and 4-coordinated ones. ReaxFF molecular dynamics simulations showed that at the top areas of the pyramid-shaped protrusions, 1- and 2-coordinated C atoms with a higher etching priority remained dominant during plasma-AEP, leading to the preferential removal of C atoms forming these protrusions. Furthermore, contact polishing was added to complete the finishing of the PCD film, followed by plasma-AEP, resulting in a nanoscale smooth surface with a roughness of 3.4 nm. Transmission electron microscopy confirmed that the crystal structures on the surface and subsurface of the PCD film were well ordered. Overall, this paper displays that plasma-AEP is a promising approach for highly efficient semi-finishing of PCD films. [Display omitted] • Plasma anisotropic etching polishing (plasma-AEP) is developed. • Preferential removal of protrusions on polycrystalline diamond (PCD) is confirmed. • The anisotropic etching characteristic is revealed by multi-scale simulations. • Plasma-PAE is generic for semi-finishing PCD with various thicknesses. • Contact polishing is added to achieve nanoscale finishing of PCD. [ABSTRACT FROM AUTHOR]

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Rhombohedral polytype transition metal dichalcogenide (TMDC) multilayers exhibit non-centrosymmetric interlayer stacking, which yields intriguing properties such as ferroelectricity, a large second-order susceptibility coefficient χ (2) , giant valley coherence, and a bulk photovoltaic effect. These properties have spurred significant interest in developing phase-selective growth methods for multilayer rhombohedral TMDC films. Here, we report a confined-space, hybrid metal-organic chemical vapor deposition method that preferentially grows 3R-WS 2 multilayer films with thickness up to 130 nm. We confirm the 3R stacking structure via polarization-resolved second-harmonic generation characterization and the 3-fold symmetry revealed by anisotropic H 2 O 2 etching. The multilayer 3R WS 2 shows a dendritic morphology, which is indicative of diffusion-limited growth. Multilayer regions with large, stepped terraces enable layer-resolved evaluation of the optical properties of 3R-WS 2 via Raman, photoluminescence, and differential reflectance spectroscopy. These measurements confirm the interfacial quality and suggest ferroelectric modification of the exciton energies.

The polarization wake‐up process is demonstrated here for ferroelectric switching in epitaxial Al0.93B0.07N films on W coated c‐axis oriented Al2O3 (sapphire) substrates. During the wake‐up process, the remanent polarization grows from ≈0 to >100 µC cm−2. As it does so, both the reversible and irreversible Rayleigh coefficients rise substantially, suggesting that the concentration of mobile interfaces that separate regions of opposite dipole orientation is increasing. The irreversible Rayleigh coefficient is very small (≈3.5 × 10−4 cm kV−1), four to five orders of magnitude below those of perovskite ferroelectric films such as PbZr0.52Ti0.48O3. These small values are consistent with the high coercive fields observed in the nitride ferroelectrics. The temperature dependence of the Rayleigh coefficients suggests that the interface motion is thermally activated. On increasing frequency, the Rayleigh coefficients drop, suggesting time‐dependent pinning processes also occur in this family of materials. With information from anisotropic etching experiments upon field‐cycling, a self‐consistent model that describes a polar domain microstructure evolution process during wake‐up is proposed. [ABSTRACT FROM AUTHOR]

Regarding the reverse process of materials growth, etching has been widely concerned to indirectly probe the growth kinetics, offering an avenue in governing the growth of two-dimensional (2D) materials. In this work, interface-driven anisotropic etching mode is demonstrated for the first time to be generally applied to 2D heterostructures. It is shown that the typical in-plane graphene and hexagonal boron nitride (h-BN) heterostructures follow a multi-stage etching behavior initiated first along the interfacial region between the two materials and then along edges of neighboring h-BN flakes and finally along central edges of h-BN. By accurately tuning etching conditions in the chemical vapor deposition process, series of etched 2D heterostructure patterns are controllably produced. Furthermore, scaled formation of graphene and h-BN heterostructures arrays has been realized with full assist of as-proposed etching mechanism, offering a direct top-down method to make 2D orientated heterostructures with order and complexity. Detection of interface-driven multi-staged anisotropic etching mode will shed light on understanding growth mechanism and further expanding wide applications of 2D heterostructures. [ABSTRACT FROM AUTHOR]

We demonstrate a facile and safe anisotropic gas etching technique for β-Ga2O3 under atmospheric pressure using forming gas, a H2/N2 gas mixture containing 3.96 vol% H2. This etching gas, being neither explosive nor toxic, can be safely exhausted into the atmosphere, simplifying the etching system setup. Thermodynamic calculations confirm the viability of gas-phase etching above 676°C without the formation of Ga droplets. Experimental verification was achieved by etching (1¯02) β-Ga2O3 substrates within a temperature range of 700–950°C. Moreover, selective-area etching using this method yielded trenches and fins with vertical and flat sidewalls, defined by (100) facets with the lowest surface energy density, demonstrating significant anisotropic etching capability. [ABSTRACT FROM AUTHOR]

The design and fabrication of PEDOT:PSS/n-Si cell have been widely studied in recent years, yet few studies have looked into the effect of Si substrate properties on device's performance. In this study, the thinning treatment of silicon substrates based on simple and low-cost alkaline etching has been systematically investigated. It is found that the KOH etching could effectively remove the surface damage layer. The series resistance (Rs) of device can be adjusted by silicon wafer thickness, under the optimized etching condition, the power conversion efficiency (PCE) of resulting 338 μm-thick PEDOT:PSS/n-Si could reach up to 5.17%, which is 1.7-times increase by comparing that of 500 μm-thick PEDOT:PSS/n-Si (PCE:2.97%).Furthermore, KOH-isopropanol texturing was incorporated into thinning silicon wafer, the smoothing pyramid structures can further reduce light reflectance and improve the junction contact quality between PEDOT:PSS film and n-Si substrates, and the PCE of 5.49% was finally achieved. This study shows guide value for understanding the influence of substrate thickness and texturing treatment on the performance of PEDOT:PSS/n-Si solar cell. [ABSTRACT FROM AUTHOR]

Bare chemical vapor deposition (CVD) grown graphene (GRP) was anisotropically etched with various etching parameters. The morphological and structural characterizations were carried out by optical microscopy and the vibrational properties substrates were obtained by Raman spectroscopy. The ammonia adsorption and desorption behavior of graphene-based sensors were recorded via quartz crystal microbalance (QCM) measurements at room temperature. The etched samples for ambient NH3 exhibited nearly 35% improvement and showed high resistance to humidity molecules when compared to bare graphene. Besides exhibiting promising sensitivity to NH3 molecules, the etched graphene-based sensors were less affected by humidity. The experimental results were collaborated by Density Functional Theory (DFT) calculations and it was shown that while water molecules fragmented into H and O, NH3 interacts weakly with EGPR2 sample which reveals the enhanced sensing ability of EGPR2. Apparently, it would be more suitable to use EGRP2 in sensing applications due to its sensitivity to NH3 molecules, its stability, and its resistance to H2O molecules in humid ambient. [ABSTRACT FROM AUTHOR]

Micro-electromechanical system (MEMS) fabrication has gained popularity as a means of etching silicon substrates. This paper discusses the surface texturization of a U-grooved structure by a very simple and cost-effective technique for use as a U-grooved metal--semiconductor--metal (UMSM) photodetector with aluminum/n-Si/aluminum materials. A series of etching experiments were carried out involving the addition of ammonium peroxodisulfate [(NH4)2SO4] at different concentrations to tetramethyl ammonium hydroxide (TMAH)/silicic acid etching solution, also called dual-doped TMAH. It was found that the addition of 11.5 g/l (NH4)2SO4 to TMAH/silicic acid enhances the smoothness of the surface and prevents the unwanted etching of exposed aluminum. We utilized dual-doped TMAH in the fabrication of a nanostructure in a U-grooved photodetector and found that the U-grooved photodetector has a ~59% higher photocurrent than that of a planar photodetector. The U-grooved photodetector demonstrates that increasing the light-detecting area results in high photocurrent performance for high-efficiency optical devices. [ABSTRACT FROM AUTHOR]

Micro-pyramidal structures have been synthesized on the single crystalline silicon (Si) substrate, using anisotropic etching in the potassium hydroxide (KOH) solution in the presence of the isopropyl alcohol (IPA) as the additive. Effect of the different parameters such as the concentrations of KOH and IPA and temperature on the etching process has been studied. Extracted results show that higher concentrations of the KOH and IPA, as well as the increasing temperature, lead to the larger pyramidal structures and less uniformity in their size and distributions. Incorporation of the porosity to the Si surface, before etching in the KOH solution can enhance the uniformity of the formed pyramidal structures. To the best of our knowledge, in this paper for the first time, we survey effects of the porosity which is created by the metal assisted chemical etching (MACE) method, on the formation of the micro-pyramids. Performing thermal treatment on the produced silver mask during MACE process before etching process, improves uniformity of the synthesized pyramids. For studying morphology of the formed structures, we use the field-emission scanning electron microscope (FE-SEM) images. Moreover hydrophilic behavior of the pyramidal structures has been studied. Contact angle test results show that more uniformity in the size and distribution of the structures, enhances the hydrophilicity of the surface

Traditional methods for synthesizing InGaN quantum dots (QDs), such as the Stranski-Krastanov growth, often result in QD ensembles with low density and non-uniform size distribution. To overcome these challenges, forming QDs using photoelectrochemical (PEC) etching with coherent light has been developed. Anisotropic etching of InGaN thin films is demonstrated here with PEC etching. InGaN films are etched in dilute H2SO4 and exposed to a pulsed 445 nm laser with a 100 mW/cm2 average power density. Two potentials (0.4 V or 0.9 V) measured with respect to an AgCl|Ag reference electrode are applied during PEC etching, resulting in different QDs. Atomic force microscope images show that while the QD density and sizes are similar for both applied potentials, the heights are more uniform and match the initial InGaN thickness at the lower applied potential. Schrodinger-Poisson simulations show that polarization-induced fields in the thin InGaN layer prevent positively charged carriers (holes) from arriving at the c-plane surface. These fields are mitigated in the less polar planes resulting in high etch selectivity for the different planes. The higher applied potential overcomes the polarization fields and breaks the anisotropic etching.

We demonstrate a facile and safe anisotropic gas etching technique for β-Ga 2 O 3 under atmospheric pressure using forming gas, a H 2 /N 2 gas mixture containing 3.96 vol% H 2 . This etching gas, being neither explosive nor toxic, can be safely exhausted into the atmosphere, simplifying the etching system setup. Thermodynamic calculations confirm the viability of gas-phase etching above 676°C without the formation of Ga droplets. Experimental verification was achieved by etching ( 1 - 02) β-Ga 2 O 3 substrates within a temperature range of 700-950°C. Moreover, selective-area etching using this method yielded trenches and fins with vertical and flat sidewalls, defined by (100) facets with the lowest surface energy density, demonstrating significant anisotropic etching capability., Competing Interests: No potential conflict of interest was reported by the author(s)., (© 2024 The Author(s). Published by National Institute for Materials Science in partnership with Taylor & Francis Group.)

We introduce a novel technique for thermal catalytic etching of single-crystal diamond under hydrogen atmosphere using a double-metal layer consisting of two different metallic thin films. Surface phenomena, catalytic activity, hydrogen pressure dependence and etch rates in several double-metal layer configurations were investigated. We observe that etching with an optimized thickness ratio of Ni/Pd films increases the etch rate by a factor up to 11 compared to etching with a single-metal layer Ni film. The proposed double-metal layer technique enhances hydrogen absorption, which contributes to an increased etch rate of the process, as compared to conventional single-metal layer thermal catalytic etching. Moreover, the etched pattern shows smooth (111) plane sidewalls and flat (100) step-terrace bottom features. [Display omitted] • The Ni/Pd double-metal layer improves the etch rate in thermal catalytic etching of SCD diamond at high temperature and low hydrogen pressure. • Using an optimized Ni/Pd film increases the etch rate by a factor up to 11 compared to etching with a Ni film. • The double-metal layer forms a Ni Pd solid solution that improves hydrogen absorption to enhance the etch rate. [ABSTRACT FROM AUTHOR]

Diamonds exhibit a unique combination of numerous excellent physical and chemical properties, such as the highest hardness, high Young's modulus, wide bandgap, high carrier mobility, negative electron affinity, and high thermal conductivity. Especially, diamond has attracted significant attention in recent years for its outstanding performance in high-frequency and high-power electronic devices and thermal management. Inheriting the intrinsic physical and chemical properties of diamonds, one-dimensional (1D) diamond nanostructures exhibit many additional properties that are unavailable for bulk diamond or thin films, e.g., large specific surface area, ultrahigh elasticity, and some plasticity, tip effect as well as direct transport for photon or photo-induced carriers. These properties make 1D diamond nanostructures an ideal candidate for applications ranging from micro/nano-electromechanical systems (MEMS/NEMS) to field electron emission, optical, electrochemical, and biological areas. This review will first introduce the development of controlled synthesis methods of 1D diamond nanostructure, including bottom-up chemical vapor deposition growth and top-down selective etching of bulk diamond. Subsequently, we will summarize recent advances in the mechanical, electron field emission, optical, and biological properties of 1D diamond nanostructures and their applications in electron and photon emitter, MEMS, sensing, intracellular delivery, etc. [Display omitted] [ABSTRACT FROM AUTHOR]

In this paper, we report a bionic olfactory sensor that could be applied for breast cancer detection. This paper mainly focuses on describing the basic principle of the bionic olfactory sensor and introducing the simulation-based design of the sensor. We use an original anisotropic quartz etching simulation system to simulate the etching process of the key parts of the resonator, and thus obtain the key parameters of the quartz etching process of the resonator, so as to control the production accuracy of the quartz resonator and improve the performance of the bionic olfactory sensor. [ABSTRACT FROM AUTHOR]

A facile anisotropic surface modification and etching strategy is presented for the synthesis of hollow structured ZIF‐67 nanoframes. The strategy uses structural and compositional distinctions between each crystallographic facet of truncated rhombic dodecahedrons ZIF‐67 (tZIF‐67 RDs) and the moderate coordinating and etching effects of cyanuric acid (CA). The CA can anisotropically modify and protect the {110} facets from etching, causing the six {100} facets be selectively etched via an inside‐out manner, and finally forming the hollow nanoframes. The surface‐modified hollow tZIF‐67 RDs can be facet‐selectively etched by metal salts in an outside‐in manner to give metal‐doped tZIF‐67 nanoframes. After calcination, the metal‐tZIF‐67 hybrids are converted into metal‐Co alloy/C composite catalysts with hollow nanoframed structures. The PtCo/C catalyst with only 5.9 wt % Pt exhibits high catalytic activities and stabilities in the hydrogen evolution reaction (HER) in acidic solutions. [ABSTRACT FROM AUTHOR]

Silicon bulk etching is an important part of micro-electro-mechanical system (MEMS) technology. In this work, a novel etching method is proposed based on the vapor from tetramethy-lammonium hydroxide (TMAH) solution heated up to boiling point. The monocrystalline silicon wafer is positioned over the solution surface and can be anisotropically etched by the produced vapor. This etching method does not rely on the expensive vacuum equipment used in dry etching. Meanwhile, it presents several advantages like low roughness, high etching rate and high uniformity compared with the conventional wet etching methods. The etching rate and roughness can reach 2.13 µm/min and 1.02 nm, respectively. Furthermore, the diaphragm structure and Al-based pattern on the non-etched side of wafer can maintain intact without any damage during the back-cavity fabrication. Finally, an etching mechanism has been proposed to illustrate the observed experimental phenomenon. It is suggested that there is a water thin film on the etched surface during the solution evaporation. It is in this water layer that the ionization and etching reaction of TMAH proceed, facilitating the desorption of hydrogen bubble and the enhancement of molecular exchange rate. This new etching method is of great significance in the low-cost and high-quality micro-electromechanical system industrial fabrication. [ABSTRACT FROM AUTHOR]

Atomically thin solid-state channels enabling selective molecular transport could potentially be used in a variety of separation and energy conversion applications. The density of channels, their height, distance and edge structure are the key factors that dramatically impact the selective transport performance. However, such channels with small constrictions and atomic precision have been limited to proof-of-concept demonstrations based on microscale two-dimensional (2D) crystal stripes. Here, we report the engineering of highly ordered, scalable monolayer graphene crystallite arrays by chemical vapor deposition (CVD) method with a modified anisotropic etching approach. The size, shape, distance and edge structure of the graphene crystallite arrays in a large area could be delicately controlled through tailoring the synthetic parameters. This array structure can act as pillars to prop up a smooth single-crystal graphene film, and the fabricated integrated angstrom-size (3.4 Å) channels allow water transport but exclude hydrated ions, demonstrating potential in selective ionic sieving and nanofiltration practice. [ABSTRACT FROM AUTHOR]

Peculiar zigzag-like Prussian blue analogue was created by anisotropic etching of PBA arising from inhomogeneous spatial distribution of FeIII during ions doping. • Zigzag-like Prussian blue analogue was created by anisotropic etching of PBA. • It arose from inhomogeneous spatial distribution of FeIII by ions doping. • The open "Z" structure endowed the catalyst with promising catalytic efficiency. Nanoscale metal–organic frameworks (nano-MOFs) with unique open architectures offer great advantages for constructing fascinating functional materials, but their configurations are largely limited to mesoporous or hollow structures. Both the rational design of nano-MOFs with sophisticated structures and the comprehensive knowledge of their formation mechanism remain an interesting research topic. In this work, we reported a highly peculiar zigzag crystal of a Prussian blue analogue (PBA) bearing the ensemble of walls with uniform thickness (∼60 nm) in three-dimensional space. Such "Z"-like PBA was acquired by the preferential etching of two opposing corners of its parent NiCo-PBA cubes that was pre-doped by metal ligand ions (i.e. , [Fe(CN) 6 ]3−). Mechanistic studies suggested that the anisotropic etching seemed to arise from the heterogeneous growth and inhomogeneous spatial distribution of the FeIII and FeII (stemming from redox reaction of FeIII) species, even though all the metal elements (including Fe, Co, and Ni) were evenly dispersed in each individual cube as indicated by HAADF-STEM and linear EDS scan analyses. The open "Z" structure provided larger surface area and a greater number of active sites to activate reagents in catalytic reaction and enhanced the degradation efficiency in removing bisphenol A from aqueous solution with PMS. The current findings are expected to pave way for a fine tuning the structures and properties of MOFs, and encourage extended research on developing novel anisotropic crystals. [ABSTRACT FROM AUTHOR]

The fabrication of sharp tips manufactured using silicon or using a silicon mold is a widely used method with a wide range of applications. In this study, we extend our work on the fabrication of tetrahedral molds in (111) silicon and the fabrication of tips based on those molds. We present multiple strategies to make a range of different structures out of silicon-rich nitride, focusing on an approach that takes advantage of oxidation sharpening to improve both the aspect ratio and the tip radius, as well as to make the fabrication process both more efficient and versatile. In this way, single tips and so-called tripod tips with a radius of less than 3 nm are successfully fabricated and used in an AFM probe to show the functionality of the tips. [ABSTRACT FROM AUTHOR]

The influence of various etching processes on the single-crystalline (100) silicon surface is studied. It is demonstrated that microstructuring of the surface of high-resistivity single-crystalline silicon in alkaline solutions is better performed using electrolytic methods at temperatures no lower than 80°C. Etch patterns with better-defined side faces are formed by anisotropic etching with the addition of hydrogen peroxide. [ABSTRACT FROM AUTHOR]

The article discusses a study that described a method of generating platinum electrodes with a porous surface by anisotropic etching. Topics include the development of the electrode for a suprachoroidal retinal prosthesis, the use of a scanning electron microscope to observe the surface of the electrode after etching, and the use of a custom-made stimulator for the application of symmetric cathodic-first biphasic current pulses.

Graphical abstract Fast and maskless nanofabrication for high-quality nanochannels. Highlights • This novel approach provides a fast, maskless and nondestructive fabrication strategy for high-quality nanochannels. • The proposed fabrication method eliminates the limitation of HF/HNO 3 mixtures in nanofabrication. • The morphology of nanochannels can be controlled by changing the concentration of etchant and scratching load. • The nanofluidic chips fabricated by proposed method provide a good platform for nanofluid analysis. Abstract Nanochannels are critical components for the fundamental and applied studies of nanofluids. However, the intrinsic low efficiency and high cost of conventional bulk-/surface-/mold-machining methods severely hinder the wide application of nanochannels. Here, we reported a fast, low-cost and maskless fabrication strategy based on friction-induced selective etching in HF/HNO 3 mixtures for controllable preparation of diversified and high-quality Si nanochannels. Owing to its distinct anisotropic etching characteristic to scratched area, this novel integrated fabrication process eliminated the limitation of HF/HNO 3 mixtures in nanofabrication. Particularly, the etching efficiency and depth of scratched Si in HF/HNO 3 mixtures are 12 and 2 times of those in HF solution, respectively. Furthermore, the effects of the volume ratio of HF and HNO 3 as well as scratching parameters on nanochannel fabrication were investigated systematically. Cross-sectional transmission electron microscopy observation indicated that the as-fabricated nanochannels have no structural damage. Finally, the corresponding nanofluidic device was designed, fabricated and verified in sequence. The results demonstrate the feasibility of proposed approach for nanochannel fabrication in the area of nanofluids, particularly in analytical chemistry, biochemistry, liquid transport and metering, and energy conversion. [ABSTRACT FROM AUTHOR]

Abstract Two-dimensional layered molybdenum disulfide (MoS 2) is a promising catalyst for hydrogen evolution reaction (HER), and a good replacement for platinum (Pt) in elelctrochemical water splitting. Most transition metal dichalcogenides (TMDs) show excellent catalytic activity, which stems from their active sites located along the edges. However, small density of the active sites in the basal plane, largely limits TMDs performance. To enhance the HER catalysis activity of MoS 2 , we developed an efficient and scalable approach to significantly increase the overall electrochemically active sites using mild sodium hypochlorite (NaClO) solution anisotropic etching. The effect is further enhanced by oxygen-plasma pretreatment of the material, which - upon chemical etching - leads to highly porous and highly reactive structure. The resulting chemically activated MoS 2 (ca-MoS 2) was systematically characterized and optimized. The optimized ca-MoS 2 powder exhibits enhanced HER performance with an overpotential of 0.34 V at a current density of 0.5 mA cm−2 in this experiment due to the increasing active sites, and the Tafel slope also smaller than other samples. This chemical etching method provides new ways to design atomic structure modification, including controlling layered TMD electrochemical property and new type of transistor fabrication. Graphical abstract fx1 Highlights • A simple and non-aggressive chemical method to etch MoS 2 anisotropically was developed. • Chemical activation firstly occurred on MoS 2 edges, and new etched edges with armchair structure were formed. • Controllable triangle pits with high density on MoS 2 basal plane were produced with O 2 plasma pretreatment. • Chemical activated MoS 2 has high density active sites for hydrogen evolution reaction. [ABSTRACT FROM AUTHOR]

Graphene with atomically smooth and configuration-specific edges plays the key role in the performance of graphene-based electronic devices. Remote hydrogen plasma etching of graphene has been proven to be an effective way to create smooth edges with a specific zigzag configuration. However, the etching process is still poorly understood. In this study, with the aid of a custom-made plasma-enhanced hydrogen etching (PEHE) system, a detailed graphene etching process by remote hydrogen plasma is presented. Specifically, we find that hydrogen plasma etching of graphene shows strong thickness and temperature dependence. The etching process of single-layer graphene is isotropic. This is opposite to the anisotropic etching effect observed for bilayer and thicker graphene with an obvious dependence on temperature. On the basis of these observations, a geometrical model was built to illustrate the configuration evolution of graphene edges during etching, which reveals the origin of the anisotropic etching effect. By further utilizing this model, armchair graphene edges were also prepared in a controlled manner for the first time. These investigations offer a better understanding of the etching process for graphene, which should facilitate the fabrication of graphene-based electronic devices with controlled edges and the exploration of more interesting properties of graphene. [ABSTRACT FROM AUTHOR]

The etching of Si wafers significantly influences the efficiency of photovoltaic devices. Texturing can effectively decrease front surface reflection and improve device performance. Saw damage removal (SDR) is necessary to yields uniform random pyramidal surfaces without the appearance of saw marks, it entails significant consumption of chemical solutions and complicated cleaning steps. Herein, an alternative process of pre-texturing thermal treatment was carried out at 800 °C for 10 min, followed by anisotropic texturing, and a uniform pyramidal surface over a large area of the textured surface was obtained without saw marks. Compared with that of as-cut mono-Si wafers (30.7%), the weighted average reflectance of the samples textured with or without thermal treatment decreased to 11.2% and 11.9%, respectively, and further to 3% and 3.4%, respectively, when anti-reflection coatings were applied. In addition, saw marks on the wafer surface were used as gettering sites during thermal treatment, and the bulk lifetime was more than doubled from 42.6 µs before the treatment to 93.8 µs after. The simple, SDR-free method presented herein for enhancing the textural uniformity of Si wafers and, hence, solar cell performance, can be employed on an industrial scale without necessitating additional investment in equipment.